What is the purpose of a dedicated "Build Server"? [closed]

Question

I haven't worked for very large organizations and I've never worked for a company that had a "Build Server".

What is their purpose?
Why aren't the developers building the project on their local machines, or are they?
Are some projects so large that more powerful machines are needed to build it in a reasonable amount of time?

The only place I see a Build Server being useful is for continuous integration with the build server constantly building what is committed to the repository. Is it I have just not worked on projects large enough?

Someone, please enlighten me: What is the purpose of a build server?

Answer 1

The reason given is actually a huge benefit. Builds that go to QA should only ever come from a system that builds only from the repository. This way build packages are reproducible and traceable. Developers manually building code for anything except their own testing is dangerous. Too much risk of stuff not getting checked in, being out of date with other people's changes, etc. etc.

Joel Spolsky on this matter.

Answer 2

Build servers are important for several reasons.

• They isolate the environment The local Code Monkey developer says "It compiles on my machine" when it won't compile on yours. This can mean out-of-sync check-ins or it could mean a dependent library is missing. Jar hell isn't near as bad as .dll hell; either way, using a build server is cheap insurance that your builds won't mysteriously fail or package the wrong libraries by mistake.

• They focus the tasks associated with builds. This includes updating the build tag, creating any distribution packaging, running automated tests, creating and distributing build reports. Automation is the key.

• They coordinate (distributed) development. The standard case is where multiple developers are working on the same code base. The version control system is the heart of this sort of distributed development but depending on the tool, the developers may not interact with each other's code much. Instead of forcing developers to risk bad builds or worry about merging code overly aggressively, design the build process where the automated build can see the appropriate code and processes the build artifacts in a predictable way. That way when a developer commits something with a problem, like not checking in a new file dependency, they can be notified quickly. Doing this in a staged area let's you flag the code that has built so that developers don't pull code that would break their local build. PVCS did this quite well using the idea of promotion groups. Clearcase could do it too using labels but would require more process administration than a lot of shops care to provide.